Kinetic modeling of the biodegradation of the aqueous p-xylene in the immobilized soil bioreactor

Biodegradation kinetics of p-xylene in aqueous solution was studied in a new type of biofilm reactor—immobilized soil bioreactor. Biofilm modeling was performed in order to determine the concentration gradients within the biofilm based on a coupled diffusion-reaction model for cylindrical geometry. The total amount of biomass in the 0.83 L bioreactor changed from 460 to 780 mg during continuous operation. The concentration gradient was typical for a shallow biofilm and also predicts low mass transfer resistance within the biofilm. Rate constants for the continuous regime were determined based on the biomass growth and the amount of substrate utilization, resulting in the values of: maximum specific growth rate (μmax) of 0.0047 h−1, half saturation constant (Ks) of 3.9 mg L−1 and yield (Yx/s) of 0.05 mg biomass mg−1 substrate. For batch operation, a similar yield coefficient was assumed and the experimental data was fitted to the Monod equation. μmax of 0.0047 h−1 (similar to continuous) and Ks of 10 mg L−1 were obtained.